Ecology of Animals 657 



In some northern areas, such as sections of central Florida and 

 northwestern United States, there are extensive belts of rain forests. 

 These are characterized by a rich vegetation, an abundance of leaf mold, 

 and a great variety of animal life. 



COMMUNITY SUCCESSION 



All biotic communities are in a dynamic state, that is, they are con- 

 tinuously changing. These changes are evident from day to night, from 

 season to season, and from year to year. 



The day-to-night changes are chiefly evinced by the different ani- 

 mals which are active at the various times. Most of the mammals, for 

 example, rest during the day and emerge at night to hunt food ; most 

 birds are active chiefly during the day. The animals active at the dif- 

 ferent times vary with the community. 



Seasonal changes are most evident in those areas with marked 

 temperature variations from one season to another. This may cause 

 mass movements of animals from one area to another, the inactivity of 

 some which are in hibernation, or even a change in appearance such as 

 the color changes shown by the varying hare. 



In no way is the dynamic aspect of a community more evident than 

 in the changes which occur over a period of years. Of these changes, 

 the most pronounced one is the gradual development of all communities 

 within an association toward a single type. Within an association, this 

 ultimate development is known as the climax and remains relatively un- 

 changed so long as the climate stays the same. Within the beech-maple 

 association, all development eventually culminates in a beech-maple for- 

 est. Such a forest is known as a climax community or association. The 

 developmental stages are known as associes, and the whole series of 

 stages including the climax is known as a sere. 



Within any association there are numerous developmental stages 

 present. Very often a sere starts as a small pond or lake left behind by 

 some glacier. As the years pass, this body of water gradually fills with 

 vegetation from the edges. The initial stage or first associes will be the 

 open water with its population of sunfish, aquatic invertebrates, and 

 perhaps submerged vegetation. The next associes would occur as the 

 pond was becoming a marshy area due to the growth of cattails, arrow 

 weeds, and other vegetation. Living in this associes would be forms 

 such as the burrowing crayfish, some amphibious snails, and the mois- 

 ture-loving red-winged blackbirds. As soil forms from these pioneer 



